Research

The overall aim of my research program is to discover patterns of genetic diversity in plants across the landscape and explore the possible drivers of that diversity. My interests in the drivers of diversity fall under three main themes: 1) speciation processes, 2) biogeography, and 3) rarity. These themes are not exclusive, and there is significant overlap in how these work together to influence patterns of diversity and evolution. Of particular note in my research program is the taxonomic breadth of my investigations – I have developed extensive genetic resources and background knowledge for at least ten different species groups in six different plant families. Although each group has required a significant, independent investment of time and effort, my research into the genetic diversity in each group is united by the three main themes of my program.

Speciation processes

Polyploidy and hybridization

Species are the fundamental units of biological diversity, and speciation can be viewed as a time-extended process of divergence between evolutionary lineages. In some cases, inference of species boundaries is straightforward, based on assessments of reproductive isolation, morphological discontinuity, and genetic independence of lineages. In other cases, patterns resulting from processes such as polyploidy (whole genome duplication), hybridization, and recent divergence greatly confound the inference of species boundaries. Detailed studies at low taxonomic levels (species and populations) in groups where these confounding processes occur are fundamental to advancing our knowledge of evolution, speciation, and biological diversity. Using microsatellite markers, nuclear and chloroplast DNA sequences, and assessments of ploidy level, I am studying several different groups of plants that share these complex speciation processes.

I am evaluating the roles of hybridization, polyploidy, ecological differentiation, floral morphology and pollination biology in shaping diversity in several lineages of southwestern Phlox species (phlox family).

I am developing a comprehensive study of red-flowered hedgehog cacti from the southwest, Echinocereus section Triglochidiatus (cactus family) with a special focus on the federally endangered E. arizonicus subsp. arizonicus (Arizona hedgehog cactus).

Biogeography

Phylogeography

The arid American Southwest provides an excellent context for examining biogeographic drivers of diversification in plants. This area is: 1) the center of diversity for a number of plant groups, 2) home to a great variety of environments, topologies, habitats, substrates, local climates, and ecological interactions within relatively short distances, and 3) rich in geologic, palynologic, and macrofossil data that provide information about both deep and more recent history. I am interested in elucidating the environmental, geographical, and historical processes that have affected patterns of diversification and distribution in plants in this area using a phylogeographic approach.

Within this biogeographic context, I have examined and am in the process of examining the distribution of genetic diversity in Encelia (brittlebushes, sunflower family), Cirsium (thistles, sunflower family), and Lycium (desert thorns, tomato family), and Carnegiea (saguaro, cactus family).

With funding from the Bureau of Reclamation, I am also working collaboratively to decipher the biogeographic and historical influences on the genetic diversity of invasive Tamarix (salt cedars, tamarisk family), in order to inform ongoing biological control of this group and provide predictive management tools in the face of global climate change.

Rarity

Conservation genetics

The interdisciplinary field of conservation biology aims to provide the knowledge and tools necessary for the long-term preservation of biodiversity. Studies of population genetic diversity are one important source of information for conservation biology, and knowledge of genetic diversity within rare species is one of the three top priorities of the Convention on Biological Diversity. Population genetic studies provide fundamental information about populations of rare plants such as the amount of genetic diversity, distribution of genetic diversity within and among populations, degree of population isolation or connectedness, patterns of genetic exchange among populations, occurrence of hybridization, relative importance of inbreeding, asexual and sexual reproduction, and presence of taxonomic distinctiveness. In my research, I apply DNA sequencing and microsatellite analyses to examine genetic diversity in populations of rare and endangered plants. Some of my current projects within the context of rarity include the: